Its very convenient when you think of something that needs testing but which cannot be tested yet for some reason. A bit like making a note in your project todo list except in this case you won't be able to ignore or lose the note: each time you run your tests in the NUnit gui the ignored tests and the overall progress/success bar are marked in yellow instead of the usual green for sucess. This is much better than commenting out code in a test harness where it is likely to be forgotten.